Violation of NEC by quantum states of matter in curved spacetimes put a restriction on the possible quantum states of matter which lead to the stable configuration (see [1]}, [2]}, [3]}). It is also shown in [1]} that even if a violation of NEC occurs in stable quantum matter, it leads to modes with superluminal propagation. This violates causality. Further, dynamical violation of NEC is another important aspect in cosmological models, discussed in [5]}.
